Sucker-Rod Pumping Handbook Production Engineering Fundamentals and Long-Stroke Rod Pumping Gabor Takacs, PhD Petroleum Engineering Department, University of Miskolc, Hungary AMSTERDAM(cid:129)BOSTON(cid:129)HEIDELBERG(cid:129)LONDON NEWYORK(cid:129)OXFORD(cid:129)PARIS(cid:129)SANDIEGO SANFRANCISCO(cid:129)SINGAPORE(cid:129)SYDNEY(cid:129)TOKYO GulfProfessionalPublishingisanimprintofElsevier GulfProfessionalPublishingisanimprintofElsevier 225WymanStreet,Waltham,MA02451,USA TheBoulevard,LangfordLane,Kidlington,Oxford,OX51GB,UK Copyright©2015ElsevierInc.Allrightsreserved. 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Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgeinevaluatingandusing anyinformation,methods,compounds,orexperimentsdescribedherein.Inusingsuchinformationormethods theyshouldbemindfuloftheirownsafetyandthesafetyofothers,includingpartiesforwhomtheyhavea professionalresponsibility. Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors,assumeany liabilityforanyinjuryand/ordamagetopersonsorpropertyasamatterofproductsliability,negligenceor otherwise,orfromanyuseoroperationofanymethods,products,instructions,orideascontainedinthe materialherein. ISBN:978-0-12-417204-3 LibraryofCongressCataloging-in-PublicationData AcataloguerecordforthisbookisavailablefromtheLibraryofCongress BritishLibraryCataloguing-in-PublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary ForinformationonallGulfProfessionalPublishingpublications visitourwebsiteathttp://store.elsevier.com/ Preface Thisbookretainsthebasicstructureandapproachofmy“ModernSucker-RodPumping”publishedby PennWellBooksin1993butisacompletelyupdatedandenlargedversionoftheoriginal.Sucker-rod pumping,althougha150-year-oldtechnology,stillcontinuouslyevolves;newequipment,newproce- dures,andnewoptimizationschemesappeareveryday,ofwhichpracticingengineersmustbeaware. Iwantedtohelpanyoneinterestedinthistechnologybypresentingthestateoftheartofmodern-day sucker-rodpumpingtheoriesandpractices.ForthisreasonIdiligentlyresearchedtheliteraturefornew developmentsthroughouttheyearssothatnosignificantcontributiontoourindustrycouldescapemy attention.Proofofthisisthetotalnumberofreferencescitedinthetext,whichamountstoalmost400. Havingspentmostofmycareerinacademiaandregularlyteachingindustryshortcoursesonarti- ficiallifttopics,Ifullyunderstandtheimportanceofhavingpropertextbooks.WhenIwaspreparing thisvolume,oneofmyobjectiveswastoprovidethetraineeaswellastheexperiencedengineerwitha comprehensive textbook. The book follows the systematic way of teaching new material: after covering the fundamentals of production engineering the different components of the equipment and their features are introduced, then basic design and selection procedures are covered. Advanced topics like optimization and analysis are fully explained with worked examples. The book can be usedattheundergraduateandgraduatelevels,aswellasinindustrialtrainingofbasicandadvanced topics. All phases of rod pumping are introduced by presenting the technical background first; then the most significant technical and theoretical developments are fully covered. This approach ensures that the book can serve as a complete reference to its topic. Since design of individual parts and of the total pumping system iscovered as well, one can utilize the book for solving mostof the design problems encounteredinpractice. Newtechnological developmentsinthe last twentyyearshavesignificantlywidenedthe applica- tionrangesofsucker-rodpumping,andtodaydeeperwellswithgreaterliquidratescanbeproduced thaneverbefore.Inadditiontonewmaterialsandinnovativeequipmentcoveredinthebook,Ichoseto presentlong-strokerodpumpinginaseparatechapter,neverpublishedbeforebyanyoneelse.Thetwo maintypesoftechnologiesavailabletodayareintroducedandtheirtechnicalandoperationalfeatures are described indetail. April 2015 Gabor Takacs xi CHAPTER 1 INTRODUCTION TO SUCKER-ROD PUMPING CHAPTER OUTLINE 1.1 ArtificialLiftMethods.......................................................................................................................1 1.1.1 GasLifting...................................................................................................................2 1.1.2 Pumping......................................................................................................................2 1.1.3 ArtificialLiftPopulations..............................................................................................3 1.2 ComparisonofLiftMethods...............................................................................................................4 1.2.1 LiftingCapacities.........................................................................................................4 1.2.2 SystemEfficiencies......................................................................................................5 1.2.3 FurtherConsiderations..................................................................................................6 1.3 MainFeaturesofSucker-RodPumping...............................................................................................7 1.3.1 ShortHistory................................................................................................................7 1.3.2 Applications.................................................................................................................9 1.3.3 Advantages,Limitations..............................................................................................11 References............................................................................................................................................12 1.1 ARTIFICIAL LIFT METHODS Usually,oilwellsintheearlystagesoftheirlivesflownaturallytothesurfaceandarecalledflowing wells.Flowingproductionmeansthatthepressureatthewellbottomissufficienttoovercomethesum ofpressurelossesoccurringalongtheflowpathtotheseparator.Whenthiscriterionisnotmet,natural flowends andthewell dies. The two main reasonsfor awell’s dying are: • itsflowing bottom hole pressure drops belowthe total pressure losses inthewell; or • pressurelossesinthewellbecomegreaterthanthebottomholepressureneededformovingthe well stream tothe surface. Thefirstcaseoccursduetotheremovaloffluidsfromtheundergroundreservoir;thesecondcase involves anincreasingflowresistance inthewell. This can becausedby: • an increasein the density of the flowingfluidasa result of decreased gas production; or • various mechanical problems likea small tubing size, downhole restrictions,etc. Artificialliftingmethodsareusedtoproducefluidsfromwellsthatarealreadydeadortoincrease theproductionratefromflowingwells.Theimportanceofartificialliftingisclearlyseenfromthetotal 1 Sucker-RodPumpingHandbook.http://dx.doi.org/10.1016/B978-0-12-417204-3.00001-7 Copyright©2015ElsevierInc.Allrightsreserved. 2 CHAPTER 1 INTRODUCTION TO SUCKER-ROD PUMPING number of installations: according to one estimate there are approximately two million oil wells worldwide, of which about 50% are placed on some kind of artificial lift [1]. There are several lifting mechanisms available for the production engineer to choose from. One widely used group of artificial lift methods uses some kind of a pump set below the liquid level to increasethepressureofthewellstreamsoastoovercomethepressurelossesoccurringalongtheflow path.Otherliftingmethodsusecompressedgas,injectedfromthesurfaceintothewelltubingtohelp the lifting of well fluids tothe surface. Although all artificial lift methods could be grouped based on the two basic mechanisms just discussed, their traditional classification is somewhatdifferent, asdiscussed inthe following. 1.1.1 GAS LIFTING Allversionsofgasliftingusehigh-pressuregas(inmostcasesnaturalgas,butothergaseslikeN or 2 CO canalsobeused)injectedinthewellstreamatsomedownholepoint.Incontinuous-flowgaslift, 2 a steady rate of gas is injected in thewell tubing, aerating the liquid and thus reducing the pressure lossesoccurringalongtheflowpath.Duetothereductionofflowresistance,thewell’soriginalbottom hole pressure becomes sufficient to move the gas/liquid mixture to the surface and thewell starts to flow again. Therefore, continuous-flow gas lifting can be considered as the continuation of flowing production. In intermittent gas lift, gas is injected periodically into the tubing string whenever a sufficient lengthofliquidhasaccumulatedatthewellbottom.Arelativelyhighvolumeofgasinjectedbelowthe liquidcolumnpushesthatcolumntothesurfaceasaslug.Gasinjectionistheninterrupteduntilanew liquidslugofthepropercolumnlengthbuildsupagain.Productionofwellliquids,therefore,isdone bycycles.Theplunger-assistedversionofintermittentgaslift,a.k.a.plungerlift,usesaspecialfree plunger traveling in the well tubing and inserted just below the accumulated liquid slug in order to separatetheupward-movingliquidfromthegasbelowit.Theseversionsofgasliftphysicallydisplace theaccumulatedliquidsfromthewell,amechanismtotallydifferentfromthatofcontinuous-flowgas lifting. 1.1.2 PUMPING Pumpinginvolvestheuse ofadownhole pump toincreasethepressureinthewelltoovercomethe sumofflowingpressurelossesoccurringalongtheflowpathuptothesurface.Pumpingcanbefurther classifiedusingseveraldifferentcriteria,e.g.,theoperationalprincipleofthepumpused.However,the generallyacceptedclassificationisbasedonthewaythedownholepumpisdrivenanddistinguishes between rodand rodless pumping. Rodpumpingmethodsutilizeastringofmetalrodsconnectingthedownholepumptothesurface driving mechanism which, depending on the type of pump used, generates an oscillating or rotating movement. Historically, the first kinds of pumps to be applied in water and oil wells were of the positive-displacementtype,requiringanalternatingverticalmovementtooperate.Thedominantand oldesttypeofrodpumpingiswalking-beampumping,orsimplycalledsucker-rodpumping(SRP). Itusesapositive-displacementplungerpumpanditsmostwell-knownsurfacefeatureisthepumping unitfeaturinga pivotedwalkingbeam. 1.1 ARTIFICIAL LIFT METHODS 3 The need for producing deeper and deeper wells with increased liquid volumes necessitated the evolution of long-stroke sucker-rod pumping. Different units were developed with the common feature of using the same pumps and rod strings as in conventional sucker-rod pumping, but with substantiallylongerpumpstrokelengths.Thedesiredlongstrokesdidnotpermittheuseofawalking beam,andcompletelydifferentsurfacedrivingmechanismshadtobeinvented.Thebasictypesinthis classaredistinguishedaccordingtothetypeofsurfacedriveused:pneumaticdrive,hydraulicdrive,or mechanical drivelong-stroke pumping. A newly emerged rod pumping system uses a progressing cavity pump that requires the rod string to be rotated for its operation. This pump, like the plunger pumps used in other types of rod pumping systems, also works on the principle of positive displacement, but does not contain any valves. Rodless pumping methods, as the name implies, do not utilize a rod string to operate the downhole pump from the surface. Accordingly, other means (other than mechanical) are used to provideenergytothedownholepump,suchaselectricorhydraulic.Avarietyofpumptypescanbe utilized in rodless pumping installations, including centrifugal, positive displacement, or hydraulic pumps. Themostimportantkindofrodlesspumpingiselectricalsubmersiblepumping(ESP),utilizinga multistage centrifugal pump driven by an electrical motor, both contained in a single package and submerged below the fluid level in thewell. Power is supplied to the motor by an electric cable run from the surface. Such unitsare ideallysuited toproduce high liquid volumes. The other lifting systems in the rodless category all employ a high-pressure power fluid that is pumped down the hole. Hydraulic pumping was the first method developed; such units have a positive-displacementpumpdrivenbyahydraulicengine,containedinonedownholeunit.Theengine or motor provides an alternating movement necessary to operate the pump section. The hydraulic turbine-driven pumping unit consists of a multistage turbine and a multistage centrifugal pump sectionconnected inseries.Theturbine issupplied with power fluidfromthe surface and drivesthe centrifugal pump at high rotational speeds, which lifts well fluids tothe surface. Jetpumping,althoughitisahydraulicallydrivenmethodoffluidlifting,completelydiffersfrom the rodless pumping principles discussed so far. Its downhole equipment contains a nozzle through whichthepowerfluidpumpedfromthesurfacecreatesahigh-velocityjetstream.Thekineticenergy ofthisjetisconvertedintousefulworkbythejetpump,liftingthecommingledstreamofthepower fluidandthewell’sproducedliquidstothesurface.Thedownholeunitofajetpumpinstallationisthe only oil-well pumping equipment known today thatcontains no moving parts. 1.1.3 ARTIFICIAL LIFT POPULATIONS Therearenoreliableestimatesonthedistributionofeachartificialliftmethodinthedifferentpartsof theworld.Onegenerallyacceptedfactis,however,thatsucker-rodpumpinginstallationsarethemost numerous worldwide; inthe UStherewere about 350,000 such installations in2007 [1]. The charts in Fig. 1.1, available from the Artificial Lift Research and Development Council (ALRDC)webpage[2],presentestimatesonthenumberofdifferentinstallationsandtheirshareinthe world’s total oil production. As seen, there is no correlation for most of the artificial lift methods between the number ofinstallations andthe liquid volumesproduced. 4 CHAPTER 1 INTRODUCTION TO SUCKER-ROD PUMPING FIGURE1.1 Estimatesonthenumberofdifferentoilwellinstallationsandtheirshareintheworld’stotaloilproduction. 1.2 COMPARISON OF LIFT METHODS Althoughthereareothertypesofartificialliftsinadditiontothosediscussedsofar,theirimportanceis negligible.Inanycase,thereisamultitudeofchoicesavailabletoanengineerforselectingthetypeof lifttobeused.Althoughtheuseofmanyofthoseliftingmechanismsmayberestrictedorevenruled out by actual field conditions, such as well depth, production rates desired, fluid properties, etc., usually more than one lift system turns out to be technically feasible. It is then the production engi- neer’sresponsibilitytoselect thetypeofliftthatprovidesthemostprofitablewayofproducingthe desired liquid volume from the given well(s). After a decision is made on the lifting method to be applied, a complete design ofthe installation for initial and future conditions should follow. 1.2.1 LIFTING CAPACITIES In order to provide a rough comparison of the available artificial lifting methods, two figures are presented where approximate maximum liquid production rates of the different installations are given in the function of lifting depth. The lifting capacities listed are estimates based on latest in- formation, including data froma major equipment manufacturer [3]. Figure 1.2 shows three lifting mechanisms capable of producing exceptionally high liquid rates: gas lifting, electrical submersible pumping, and jet pumping. As seen, gas lifting (continuous flow) allowstheproductionofthegreatestamountsofliquidfrommediumtohighdepths.Inshallowwells likethoseusedforwatersupply,however,electricalsubmersiblepumpingiscapabletoproducerates inexcessof60,000bpd. Figure 1.3, on the other hand, includes artificial lift methods of moderate liquid production capacity: hydraulic pumping, progressive cavity pumping (PCP), rod pumping, and plunger lifting. In most cases, lifting depth has a profound importance for the liquid volume lifted, and well rates rapidlydecreaseindeeperwells.Itcanbenotedthatsucker-rodandPCPpumpsproduceverysimilar rates from the lifting depth range of 3,000–6,000 ft; this fact, combined with the much lower in- vestmentandproductioncostsofPCPinstallations,explainsthegreatpopularityofPCPpumpsover rod-pumping applicationsin recent years. 1.2 COMPARISON OF LIFT METHODS 5 FIGURE1.2 Maximumliquidcapacitiesofhigh-capacityartificialliftinstallations. FIGURE1.3 Maximumliquidcapacitiesofmoderate-capacityartificialliftinstallations. 1.2.2 SYSTEM EFFICIENCIES Theartificialliftmethodsavailabletodayofferverydifferentenergyefficiencies.Thetotalefficiency of an artificial lift installation is found from the total energy required to operate the system and the hydraulicpowerspentonliftingthefluidstothesurface.Thisefficiencyistheproductoftheindividual efficiencies of the system’s components. The decisive part of the overall efficiency is due to the 6 CHAPTER 1 INTRODUCTION TO SUCKER-ROD PUMPING effectivenessoftheliftingmechanism,e.g.,theenergyefficiencyofthepumpused,butpowerlossesin thewellandonthesurfacecanalsohaveagreatimpactonthefinalfigure.Thebasicprerequisitefor high total energyefficiency,therefore, is the application ofa highly efficient lifting mechanism. ThemostexcellentdeviceavailableforartificialliftingisthePCPpump,whichcanbemorethan 70%efficientinconvertingmechanicalenergytohydraulicwork.SincetheuseofPCPpumpsinoil wellsrequiresrelativelysimplesurfaceanddownholeinstallationswithlowlevelsofenergylossesin systemcomponents,PCPsystemsarethemostefficientamongtheartificialliftmethods.Nowonder that, wherever well conditions fall in their application ranges, the number of PCP pumping installations is growing veryfast. Next in the line, as shown in Fig. 1.4, are sucker-rod pumping and ESP installations, with maximumsystemefficienciesofabout60%.Althoughsucker-rodandESPpumpsalonecanhavequite high energy efficiencies, both lifting methods are plagued by high downhole losses in their power transmissionsystem.Inadditiontotheselosses,freegasenteringthepumpsdramaticallyreducestheir hydraulic outputand,consequently, the overall system efficiency. Hydraulic pumping installations utilizing positive displacement pumps usually have power effi- ciencies around 50%. Jet pumping and continuous-flow gas lifting are relatively low-efficiency arti- ficialliftmethods,withmaximumsaround30%.Intermittentgaslifthasthelowestenergyefficiency among the availablelift methods. 1.2.3 FURTHER CONSIDERATIONS Theselectionoftheproperliftingmethodforagivenwellorfieldrequiresmorethancomparingthe production capabilities and efficiencies of the possible systems. Fluid properties, field conditions, operating and investment cost estimates, and possible production problems are all to be considered before a final decision is arrived at. Table 1.1 (modified after [3]) provides help for a preliminary selectionofpossiblecandidatesandforeliminatingthosemethodsnotsuitableforactualconditions. FIGURE1.4 Approximatesystemefficienciesofdifferentartificialliftmethods. 1.3 MAIN FEATURES OF SUCKER-ROD PUMPING 7 Table1.1 Mainfeaturesofartificialliftinstallations Al Gas Hydraulic Jet Plunger Method SRP lifting ESP PCP pumping pumping lift Max. 16,000 18,000 15,000 12,000 17,000 15,000 19,000 operating depth,ft Max. 6,000 50,000 60,000 6,000 8,000 20,000 400 operating rate,bpd Max. 550(cid:1) 450(cid:1) 400(cid:1) 250(cid:1) 550(cid:1) 550(cid:1) 550(cid:1) operating temp.,F Gas Fairto Excellent Fair Good Fair Good Excellent handling good Corrosion Goodto Goodto Good Fair Good Excellent Excellent handling excellent excellent Solids Fairto Good Fair Excellent Fair Good Fair handling good Fluid >8(cid:1) >15 >10(cid:1) <40(cid:1) >8(cid:1) >8(cid:1) >15(cid:1) gravity, API(cid:1) Offshore Limited Excellent Excellent Limited Good Excellent N/A application 1.3 MAIN FEATURES OF SUCKER-ROD PUMPING 1.3.1 SHORT HISTORY Duringtheearlyhistoryofmankinddifferentmethodswereusedtodeliverdrinkingwaterfromrock formationsclosetothesurface.Theseincludeddrillingandpumpingofshallowwells,probablyfirst invented by the Chinese many centuries ago. Creating plunger pumps made of bamboo pipes and valves carvedoutof stone, they used wooden rods tooperate the pump from the surface. The history of artificial lifting of oil wells had begun shortly after the birth of the petroleum in- dustry.Atthosetimes,insteadoftherotarydrillingtechniquepredominantlyusedtoday,cabletools wereusedtodrillthewells;thistechnologyreliedonawoodenwalkingbeamthatliftedanddropped thedrillingbithungonaropeorcable.Inearlytimes,thedrillingrigwasdrivenbyasteamengine. Whenthewellceasedtoflow,itwasquitesimpletousetheexistingwalkingbeamtooperateabottom- holeplungerpump.Itbecamecommonpracticetoleavethecable-tooldrillingrigonthewellsothatit could later be used for pumping. The sucker-rod pumping system was born, and its operational principles have notchanged since [4]. Although today’s sucker-rod pumping equipment does not rely on wooden materials and steam power,itsbasicpartsarestillthesameastheywerebefore;seeFig.1.5Firstofall,thewalkingbeam, the symbol of this pumping method, is still used to convert the prime mover’s rotary motion to the alternatingmotionneededtodrivethepump.Thesecondbasicpartistherodstring,whichconnects